Technikatörténeti szemle 11. (1979)
TANULMÁNYOK - Petik Ferenc: The development of material testing machines
iron in a single span of 600 ft (180 m). The committee of expert witnesses of an imposing selection of scientists could base his opinion only on experience and theoretical considerations. T. Young (1773—1829), who later became the great scientist of the strength of materials but who was not summoned at that time to witness before the committee, wrote an article in which he criticized the planned bridge scheme by scientific methods. It is characteristic for that time that the compression strength of cast iron was determined by Young by employing the following simple test: A small prismatic specimen 1/8 in x 1/8 in 1/4 in long was placed in a vice and the force needed to crush it was measured. Allowances for friction were calculated. The compression strength of cast iron determined in this way was calculated to be approximately 64 tons to the square inch (~1 kN/mm2). Breaking strength values determined by reliable testing devices were published only in 1818 by G. Rennie, but these coincided fairly well with data of Young obtained by the extemporized test. Beginnings of the testing of metals A metal testing machine was mentioned already in 1758. A Frenchman, Perronet built a machine suited for tensile, compression and bending tests. In the St. Petersbourgh Institute of Road and Railway Building Engineers structural irons used for bridge construction were tested on the tensile tester built by G. Lamé (1795—1870), the young French guest professor, in 1824 (Fig. 7). Similar machines were built by Lagerhjelm in Stockholm, and by Woolwich in London in 1832. In the Sayner Iron Works in Germany, a simple balance-type tensile tester was built in 1828. Loads of 20—25 tons were applied by weights and a lever of transmission ratio of 1 : 50. Steel specimens of 25 mm diameter were loaded by means of a drawing spindle actuated by hand wheel. J. W. Lossen built a tensile tester [7] in Germany for the chain links of a chain bridge. A chain strength tester that wias operated in Russia in 1830, is also known. At the beginning of the 19th century the development of metals testing was greatly accelerated, especially in England, in accordance with the requirements of rapidly developing railways, gun and machine manufacture. Especially complete structural elements were tested. The testing rig designed by Fairbairn for tube beams to be built into a steel bridge is shown in Fig. 8. 222 7. Tensile tester from St. Petersbourgh (Lamé, 1824)
